1. Field of the Invention
The present invention generally relates to an electrophotographic copying machine like a PPC and a method of setting a copy magnification in the photocopying machine.
2. Description of the Prior Art
A conventional electrophotographic copying machine comprises an optical system, a magnification setting device, an optical system shift device and a confirming device. The optical system is composed of a movable exposure lamp for scanning an original sheet, a first mirror for reflecting an image light emitted from the original sheet, second and third mirrors for further reflecting the image light from the first mirror, and an imaging lens and a fourth mirror passing the light from the third mirror for imaging on a photoconductor. The magnification setting device moves the lens and fourth mirror, individually, corresponding to an inputted magnification, for effecting the desired copy magnification. The optical system shift device moves the exposure lamp and first mirror together and the second and third mirrors together from their respective home positions to keep a fixed optical length between the face of the original sheet and the imaging lens during scanning of the original sheet, the optical length being based upon the set magnification. The confirming device is for confirming whether the exposure lamp and first mirror, and the second and third mirrors are in their respective home positions. In this way, the conventional electrophotographic copying machine, when a magnification is newly inputted, sets a copy magnification by moving the lens and the fourth mirror independent of the positions of the exposure lamp and first mirror, or the second and third mirrors in the optical system (see, for example, U.S. Pat. Nos. 4,837,598 and 4,843,427)
Although such a conventional electrophotographic copying machine is designed to limit the distance by which the original sheet can be scanned (the size of the original sheet) corresponding to the required copy magnification so that the optical system and the lens do not collide with each other, once a paper jam, for example, arises, the optical system is immediately stopped to cease the copying operation, and when a treatment for the paper jam is completed and the copying operations can be resumed, the optical system is once reset; specifically, the optical system returns to its home position, while the lens and the fourth mirror return to the positions whereby the copy magnification gets 100%. For example, assume that the copying operation is interrupted because of a paper jam when the copying machine is working with the copy magnification less than 100%, and after the copying function is recovered, the magnification is changed to enlarge the scale, and that after a service engineer, for example, tampers with the optical system, the lens is moved with the magnification set to enlarge the scale. In either case, the optical system might collide with the lens.
Moreover, assume that, in such a conventional electrophotographic copying machine, another copy magnification is newly inputted while the lens and fourth mirror are moving corresponding to the copy magnification previously inputted. If the lens and fourth mirror are immediately moved corresponding to the magnification newly inputted, the lens and fourth mirror might collide with each other. Hence, after they are once moved to the positions corresponding to the magnification previously inputted, the lens and fourth mirror should be moved to the positions corresponding to the magnification newly inputted. Thus, when the copy magnification is changed while the lens and fourth mirror are moving, there arises the problem that a long period of time is required until the setting of the magnification is completed.